Elimination of static electricity



R. BEACH ELIMINATION OF STATIC ELECTRICITY Sept. 28, 1948.

Filed June 27, 1945 INVENTOR fat/A J1me BY .2 ATT RNEY' Patented Sept.28, 19 48 UNlTED STATES I PATENT OFFICE Claims.

The invention here disclosed relates to the elimination, neutralizationor dissipation of static electricity.

Particular objects of the invention are to neutralize and remove staticelectricity impressed on moving surfaces, such as travelling belts orwebs.

More particularly it is a purpose of the invention to accomplish thiswithout resort to separately generated, neutralizing voltages andwithout connection of any sort to local power sources. 7

Further objects, in line with the above, are to provide electrostaticeliminating means which will be safe in every way and of a character notto injure the web or other material in case of accidental contacttherewith.

Further important objects are to provide practical and efficientelectrostatic eliminating means of simple, inexpensive form, easilyinstalled, occupying but small space, wholly automatic in its action,requiring no servicing and of a nature to last indefinitely withoutattention of any sort.

Other desirable objects and the novel features by which the purposes ofthe invention are attained are set forth or will appear in the course ofthe following specification.

The drawing accompanying and forming part of the specificationillustrates a typical practical embodiment of the invention but it is tobe appreciated that structure may be modified and changed as regards theimmediate illustration, all within the true intent and broad scope ofthe invention as hereinafter defined and claimed.

Fig. 1 in the drawing is a diagrammatic view illustrating the inventionas applied to the elimination or neutralization of the staticelectricity generated bya travelling web;

Fig. 2 is a broken cross sectional view as on substantially the plane ofline 22 of Fig. 1, illustrating details of the actual physicalstructure:

Fig. 3 is a cross sectional .view of the brush and supporting structuretaken on substantially the plane of line 3-8 of Fig. 2;

Figs. 4 and 5 are diagrammatic views illustrating the high potentialgradient of the convergent field effect attained by the use of separatetufts of wire bristles spaced from the surface of the travellingmaterial;

Figs. 6 and 'l are similar views illustrating the absence of highpotential gradient under conditions of a uniformly distributed electricfield.

Fig. 1 illustrates more or less diagrammatically a typical installationof the invention for overcoming static effects on a travelling Web ID.This web which may be any processed stock, such as rubber plystock,paper web, or various types of fabric, acquires electric charge as itleaves the supporting, guiding or processing rolls I2 over which itpasses.

These charges are neutralized in the present invention by tufts ll offine wire bristles, preferably supported in separated, relativelyinsulated relation spaced from the charged surface and electricallyconnected together and to round. While this separated relation ispreferred, the tufts may be disposed to form a continuous line ofbristles.

For practical reasons the sepanate tufts are preferably all mounted inspaced insulated relation on' a single common support, such as a bar l3of hard, kiln-dried, paraffin treated, wood or generally similardielectric material. Su'ch material has a constant insulating strengthcomparable with wax and is thus suited to the need for providing asupport of substantially constant insulating or dielectric strength of ahigh order. This provides a unitary brush structure which may be handledas such and mounted in proper spaced relation at one side of, that is,either over or under, the material being discharged.

In the illustration the brush is mounted above the web and usually thismay be preferred as themost convenient position.

Any suitable means may be employed for so mounting the brush, such as inthe illustration, brackets i4 attached to the frame or base portions I5of the machine and carrying an angle bar I6 extending across the web andto which the insulating brush bar is attached, as by screw fasteningsl'l.

Preferably and as indicated in Fig. 3, the angle bar i6 is of insulatingmaterial, such as hard fibre or the like. In place of this angle bar, asufficiently strong bar of wood or other insulating material .may beused.

The tufts of bristles are shown as mounted by having the base portionsof the same engaged in sockets l8 in the wooden or other insulatingsupporting bar l3. I

The tufts of bristles, while relatively insulated, are electricallyconnected together by a suitable conductor, which is connected toground.

A combination connecting and securing effect is accomplished in theillustration by using a flexible bare conductor wire l9 formed intoloops engaged in the tufts. -These loops, as indicated at 20, Figs. 2and 3, may be formed by doubling the wire down through openings 2| inthe top of the bar in line with the sockets l8 and, after catching suchloops in the bristle wires, pulling them back up through such holes,with intervening sections of wire left connecting the bristle securingloops to serve as a continuous connecting conductor.

One or both ends or any intermediate portion of the connecting wire isbrought out and extended to some grounded connection, for example asshown in Fig. 2, clamped to one of the bolts or screws 22 securing theangle bar on the supporting brackets l4.

The wire bristles may be of fine brass wire about 0.002" to 0.004". Thespacing of the tufts ordinarily may be about 1 to 3 inches apart and thetufts should project from the insulating support on which they aremounted usually about 1 inches orbetween 1 inch and 2 inches. Theconnecting wire should be strong enough to pull and hold the tuftsfirmly in place and heavy enough to easily carry the grounding current.The length of the brush made up of the spaced tufts should beapproximately equal to the width of the web, sheets or stock undertreatment.

The principle involved in the neutralization of the charges generated onthe moving surface is that of ionizing the molecules of air at the tipsof the fine wire bristles by virtue of an exceedingly high potentialgradient. The air ions of opposite polarity to the charges on the stockare strongly attracted to the stock, combining with them andneutralizing the charges.

To appreciate how the essential potential gradient is produced at thetips of the bristles even with relatively low voltage between thecharged stock and the grounded brush, reference is directed first toFigs. 6 and '7. These views indicate the effect of a D. C. voltage Vimpressed across two parallel plates A and B spaced the distance (1.These plates being oppositely charged, there is produced a uniformelectric field, as indicated by the uniformly spaced lines, Fig. 6. Thisfield being uniformly distributed in the space between the plates, thedistribution of the impressed voltage at any part of the. interveningspace can be designated by the potential gradient of V/d or as so manyvolts per centimeter. 'I'his voltage across the plates is distributedlineally with respect to the spacing between the plates. and hence thevoltage gradient is uniform or constant, as indicated in thecorresponding graph, Fig. '7.

Fig. 4 shows how by substituting a tuft of fine wire bristles for plateA, all the lines of electric force from plate B will converge upon theextremely small areas of the tips of the bristles. The electric fieldthen, instead of being uniformly disposed, is highly concentrated in thespace near the tips of the bristles with the gradient approximately asindicated by the graph in Fig. 5. Most of the voltage between thelectrodes is thus concentrated in the short space directly in front ofthe bristles. The voltage gradient at this location is high enough toionize the neutral molecules of air to the extent of forcing electronsout of the intervening air molecules.

Considering the process of ionization, it is known that in a neutralatom the orbital electrons, the small negative charges, arecounterbalanced by an equal number of Positive electric charges in thenucleus. In the presence of a sufficiently high electric field anelectron farthest from the nucleus may be forced out of the neutralatom, to form two ions,,one a freely moving negative ion, the electron,and the other a positive ion, which is the remainder of the atom. Theatom, having lost a negative charge, then possesses a preponderance ofpositive electricity by the amount of one unit of charge. This processof ionization of the atoms of the molecules of air by the brush of thepresent invention is attained by the high potential gradient created atthe tips of the bristles.

To maintain the convergent field essential to the high potentialgradient, it will be seen that it i important that the tips of thebristles be an appreciable distance from the charged surface, so as tocoliect'the convergent energy from an appreciable area, that the tips ofthe bristles be an appreciable distance from the support which carriesthem and that the supporting means be of.

dielectric material, so that the lines of force will concentrate on thetips of the bristles and not stray off to the support at the back of orat the sides of the bristles.

For a further understanding of the invention reference is made to thefact that with any two dissimilar substances in contact an unbalance ofatomic forces occurs at their interfacial boundary and that as a resultof this the electrons pass from the substance of higher dielectricconstant to the other. The substance receiving the electrons becomesnegatively charged and the other, by losing electrons, acquires an equalvalue of positive electrification. The voltage created between the twobythis migration of electrons is the contact difference of potential."

When the substances are separated, if one or both are insulators, theelectrons which migrated from one to the other are entrapped there andthe substances have thus acquired a certain amount of electricity. Twoother kinds of substances'would acquire a greater or a lesser charge,depending upon their physical properties,

As the charged substances are moved apart the capacitor effect betweenthem decreases and the voltage increases and to great magnitudes.

The relationship for this action may be expressed- Q-the charge C-thecapacitance from which it follows that voltage increases as separationof the plates increases, for a fixed charge Q of the condenser.

In illustration of the above, it can be considered that stock is chargedin moving over processing or idler rolls,- as in Fig. 1. When such stockis in contact with the metallic surface of a roll, the two materials,the stock and the steel of the rolls, are no closer together than thediameter of an average atom, which is 10- cm. The contact voltagebetween the two substances may be considered to be one millivolt (0.001volt), As the moving stock passes the break-away line of tengency withthe roll and separation increases 1,000 fold, the separation becomes 10"em, but the voltage. on the above relationship, will have increased1,000 fold or to one volt. As separation increases another 1,000 fold,the physical separation becomes em, but voltage has increased to 1.000volts. As the separation increases still more, say 100 fold, and becomesthe appreciable distance of one centimeter, the voltage. havingincreased one hundred fold, will be 100,000 volts.

This linear increase or voltage with distance of separation does not,however, continue indefinitely, because with further separation theelectric field becomes diverted to other parts of the condenser systemand because at these high voltages the air molecules become ionized,causing some of the condenser charges to be neutralized.

For such reasons it has been found best to locate the tips of thebristles, in most cases, about 4 to 5 inches away from the break-awayline and about 3 to 4 inches from the surface oi the stock.

Direct electrification is produced only on the side of the stock incontact with the roll. Assuming this electrification to be negative, thecharges will repel electrons from the atoms within the stock, causingthem to migrate to the opposite side of the stock. For this reason theelectrons may be neutralized on either side of the stock. since those onthe other side return to the ionized atoms within the material, so thatthe stock is no longer electrified.

The ultra sharp corner edges at the ends of the fine wire bristles, inthe arrangement of the tufts described, create a high. potentialgradient, with only a relatively small impressed voltage between thetuft and charged stock sufficient to effect ionization of the airmolecules to neutralize charges on the stock. a

The ends of the bristles or the several tufts should be approximatelythe same distance away from the stock and the ends should be far enoughaway from the dielectric support so that the convergent electric fieldsterminate on thepoint's instead of partly on the dielectric support. Theuse of insulating material for the support rather than conductivematerial maintains the convergent state and prevents distribution partlyinto the supporting structure.

Each tuft composed of many fine wires provides sufllcient mechanicalstrength but is resilient enough to avoid injury either to an operatoror to any stock that might contact it.

The metallic structure of the bristles and the 55 interconnecting wireconstitutes, in conjunction with the charged stock, an extremely smallelec trical capacitance or'condenser effect, and this is of particularimportance. Only a small amount of electrical energy can be'stored inthis small capacitance and hence if an electric spark should passbetween the charged plystock and the bristies, the energy of such sparkwould be insufficient to ignite any flammable vapor-air mixture that,might be present within the sparking zone.

where C=capacitance of the brush, and V==voltage between the brush andthe charged stock.

From this equation the voltage which would produce the minimum energy of0.001 or 10- Joule for ignition would be calculated- V=4.4 8 x10-=44,800 volts, approximately and hence Hence about 45,000 volts wouldbe the minimum voltage that would produce sufl'icient energy in a spark,if one should occur, to ignite an explosive mixture of solvent vaporsfrom a capacitor 10 of one micromicrofarad. With the brush of thisinvention, however, such a high voltage could not occur as the ionizinginfluence or the ultra high voltage gradient at the ends of the bristleswould create such copious amounts of neutralizing ions as to lower thevoltage to almost nil.

In actual practice the capacitance of the antistatic brush ofthisinvention would ordinarily be considerably less than onemicromicrofarad, and hence an even higher voltage than 45,000 would berequired to cause a hazardous spark, if one could occur. The ionizationof the ambient air produced by the high potential gradient is so intensethat sparking is practically impossible.

Being self-energized through the voltage estab- 30 lished between thecharged stock and the groundgated, yielding tufts of fine, flexible,sharp ended spring wire bristles on said insulating bar and projecting asubstantial distance away therefrom, said bristles-terminating withtheir ends all in substantially the same common plane.

means mounting said insulating bar with said substantially coplanar endsof the bristles spaced away from the charged surface a distance normallyof substantially three to four inches and sufflcient to create andmaintain intense convergent electric fields of high potential gradientfrom said charged surface to the ends of said tufts to produce copiousionization at the tips of the bristles and a conductor of small massconnecting said fin wire bristles and connected to ground, saidapparatus being thereby or low electrical capacitance and beingunconnected with any local power source.

2. The herein disclosed self-energizing apparatus for eliminating staticelectricity on an electrostatically charged surface, comprising a bar ofinsulating material having substantially constant dielectric strength ofhigh value. elongated, yielding tufts of fine, flexible, sharp endedspring wire bristles on said insulating bar and rojecting a substantialdistance away therefrom, said bristles terminating with their ends allin substantially the same common plane, means mounting said insulatingbar with said substantially coplanar'ends ofthe bristles spaced awayfrom the charged surface a distance normally of substantially three tofour inches and suiilcient to create and maintain intense convergentelectric fields of high potential gradient from said charged surface tothe ends of said tufts to pro- 7 duce copious ionization at the tips ofthe bristles and a conductor of small mass connecting said fine wirebristles and connected to ground, said apparatus being thereby of lowelectrical capacitance and being unconnected with any local powersource, said projecting tufts of the bristles being mounted inseparated, relatively insulated relation on said insulating bar spacedabout from one to three inches apart to thereby create at the respectivetufts separate convergent fields of high potential gradient.

3. The herein disclosed self-energizing apparatus for eliminating staticelectricity on an electrostatically charged surface, comprising a bar ofinsulating material having substantially constant dielectric strength ofhigh value, elongated, yielding tufts i fine, flexible, sharp endedspring wire bristles on said insulating bar and projecting a substantialdistance away therefrom, said bristles terminating with their ends allin substantially the same common place. means mounting said insulatingbar with said substantially coplanar ends of the bristles spaced awayfrom the charged surface a distance normally of substantially three tofour inches and sufficient to create and maintain intense convex-gentelectric fields of high potential gradient from said charged surface tothe ends of said tufts to produce copious ionization at the tips of thebristles and a conductor of small mass connecting said fine wirebristles and connected to ground, said apparatus being thereby of lowelectrical capacitance and being unconnected with any local powersource, said insulating bar having sockets in one side and communicatingopenings in the other'side of the same, said tufts having base portionsseated insaid sockets and said connecting conductor being a flexibl barewire extending along said other side of the bar and having loopsextending through said openings into holding engagement about said baseportions of the tufts seated in said sockets to thereby mechanicallysecure as well as to electrically connect said tufts.

4. The herein disclosed self-energizing apparatus for eliminating staticelectricity on an electrostatically charged surface, comprising a bar ofhard, kiln-dried, wax-treated wood having substantially constantdielectric strength of high value, elongated, yielding tufts of fine,flexible, sharp ended spring wire bristles on said insulating bar andprojecting a substantial distance tense convergent electric fields ofhigh potential gradient from said charged surface to the ends of saidtufts to produce copious ionization at the tips of the bristles and aconductor of small mass connecting said fine wire bristles and connectedto ground, said apparatus being thereby of low electrical capacitanceand being unconnected with any local power source.

5. The herein disclosed self-energizing apparatus for eliminating staticelectricity on an electrostatically charged surface, comprising a bar ofinsulating material having substantially constant dielectric strength ofhigh value, elongated, yielding tufts of fine, flexible sharpendedspring wire bristles on said insulatin bar and projecting asubstantial distance away therefrom, said bristles terminating withtheir ends all in substantially the same common plane, means mountingsaid insulating bar with said substantially coplanar ends of thebristles spaced away from the charged surface a. distance normally ofsubstantially three to four inches and sufilcient to create and maintainintense convergent electric fields of high potential gradient from saidcharged surface to the ends of said tufts to produce copious ionizationat the tips of the bristles and a conductor of small mass connectingsaid fin wire bristles and connected to ground, said apparatus beingthereby of low electrical capacitance and being unconnected with anylocal power source, said spring wire bristles being approximately 0.002"to 0.004 in diameter and the tufts of said bristles projecting away fromthe insulating bar a distance of approximately one to two and one-halfinches.

ROBIN BEACH.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 777,598 Chapman Dec. 13, 1904836,576 Hardwicke Nov. 20, 1906 878,273 Chapman Feb. 4, 1908 997,085O'Toole July 4, 1911 1,093,491 Smith Apr. 14, 1914 1,394,211 Morgan Oct.18, 1921 1,680,310 Wehrle Aug. 14, 1928 1,712,294 Cox May 7, 19292,023,321 Gutman Dec. 3, 1935 FOREIGN PATENTS Number Country Date107,005 Switzerland Jan. 9, 1924 581,695 France Dec. 3, 1924

